depends if they are used or not.
I would not recommend buying used HDD's. This is because the person selling it might say it works perfect but in reality it could be a drive which failed or is about to fail, which is why they are being sold. The person cannot offer proof that the HDD is in mint condition and working perfectly.
If it says its New, and in its box etc. Then you should look at who's selling it. The more reviews and the better the ratings are the more safe it is to purchase it. If its a new HDD which was taken out of a box for the picture or something then it should be ok, but the problem with HDD's is that if they are dropped the can break quite easily.
So yeh, I would say only buy if they are classified as new and sealed in the box. I purchased two SSD's over large resellers on ebay, they are perfect, but then with SSD's there is less risk of them being broken!

A while back...Long boring story, but with HDD's buy new. I know that prices are high at the moment (has a lot to do with the floods in Thailand) so if you can hold off a while, maybe wait until the new year.

i've seen some great deals at Best Buy and at Costco lately. I have been buying external drives in cases, and taking the drives out. I got a 2.5, 320gb external drive in case (seagate) for $69.00 plus tax.

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